You can create a template journal from entries in the Financial, AR, and AP ledgers. To create a template from an existing journal entry, open the entry modal from places such as the Reports>Journal Report and Financial>Journals tabs:
Once you've opened the journal you wish to create a template from, click the icon that reads "Create Template Journal" when you hover over it. This will open up a new journal modal with pre-populated data from the journal entry you had opened to create a journal from:
Once open, you can edit the data and submit like you would with any other journal.